1. Field of the Invention
The present invention relates to methods and a device for measuring the temperature of the melt surface within an apparatus for pulling a single crystal and, more particularly, to methods for measuring the temperature of the melt surface within an apparatus for pulling a single crystal wherein non-contact temperature measurement is performed and a device is used for the methods.
2. Description of the Relevant Art
Keeping the temperature of the melt surface in optimum condition during single crystal growth is needed in order to ensure the quality of the single crystal. As a precondition, it is required that the temperature of the melt surface be accurately measured. A dip-type thermocouple, a non-contact radiation thermometer, and the like have been used for measuring the temperature of the melt surface. However, in a temperature measuring method wherein the thermocouple is used, the thermocouple easily wears and has a short life span, or constituents of the thermocouple contaminate the melt, resulting in a bad influence upon the quality of a single crystal to be pulled. Therefore, it is difficult to continuously measure the temperature of the melt surface for a long period of time.
In order to cope with the problem, recently a method wherein non-contact temperature measurement of the melt surface is performed using the radiation thermometer has been frequently used. The temperature measuring method wherein the radiation thermometer is used is based on the luminance of a thermal radiation light radiated from an object of measurement being determined from the temperature and the emissivity of the object of measurement. The temperature is obtained based on the luminance of the thermal radiation light measured by non-contact measurement and the emissivity obtained on a different occasion. Therefore, in the temperature measuring method wherein the radiation thermometer is used, there is no probability that impurities will contaminate a melt. The temperature of the melt surface can be continuously measured during the pulling of a single crystal.
FIG. 1 is a diagrammatic sectional view showing an apparatus 40 for pulling a single crystal incorporating a conventional temperature measuring device 42 wherein a radiation thermometer is used, and reference numeral 11 in the figure represents a crucible. The crucible 11 is cylindrical, and is supported with an ascent/descent means (not shown) by which the crucible 11 is moved up and down while being rotated. The vertical position of the crucible 11 can be adjusted by driving the ascent/descent means. An almost cylindrical heater 12 is arranged around the crucible 11 and an electric power supply regulator 12a is connected thereto. An almost cylindrical heat insulating mold 13 is arranged around the heater 12, and a lower chamber's wall 14 is arranged around the heat insulating mold 13 so as to surround the heat insulating mold 13. An upper chamber's wall 15 stands on a lower chamber's upper wall 14a having the shape of a ring.
Inside the upper chamber's wall 15, a pulling shaft 16a is suspended. A seed crystal 16b is held by a holder 16c at the lower end of the pulling shaft 16a, which is wound while being rotated by a driving means 16. A window 41 is formed in a vertical position on a lower chamber's side wall 14b where the melt surface 17a is located, and is sealed with a quartz glass member 41a or the like.
The crucible 11 is charged with a melt 17 of melted polycrystal silicon (Si) or the like. By bringing the seed crystal 16b into contact with the melt surface 17a and pulling the pulling axis 16a while rotating it, a single crystal 18 can be grown from the melt surface 17a.
On the other hand, a radiation thermometer 43 is placed outside the window 41 in the almost horizontal direction, and is connected to a computing means 44 which is further connected to the electric power supply regulator 12a . The non-contact temperature measuring device 42 includes the radiation thermometer 43 and the computing means 44. The luminance of a thermal radiation light radiated from the heat insulating mold 13 in the vicinity of the melt surface 17a is measured using the radiation thermometer 43. The temperature is computed and detected based on the measured luminance of the thermal radiation light in the computing means 44. In the electric power supply regulator 12a, the quantity of electric power supplied to the heater 12 is regulated based on the computed and detected temperature so as to keep the melt surface 17a at a prescribed temperature. As a result, the melt surface 17a is kept at a prescribed temperature.
However, in the temperature measurement using the above temperature measuring device 42, the temperature of the heat insulating mold 13 and that of the melt surface 17a have not been the same, as the diameter of the seed crystal 18 and the apparatus for pulling a single crystal 40 have been larger in order to manufacture an LSI more efficiently. As a result, it has been difficult to accurately measure the temperature of the melt surface 17a. Since the heat capacity of the melt 17 is relatively large, there is a difference in temperature between the melt 17 in the vicinity of the crucible 11 close to the heater 12 and the melt 17 in the vicinity of the single crystal 18 away from the heater 12. As a result, it is difficult to accurately measure the required temperature of the melt surface 17a in the vicinity of the single crystal 18. Since convection is caused in the melt 17 by the difference in temperature, the temperature of the melt surface 17a easily varies with time. As a result, it is difficult to accurately measure the temperature of the melt surface 17a following the variations.
In order to cope with the above problems, it is desirable that the temperature of the melt surface 17a in the vicinity of the single crystal 18 be directly measured using the radiation thermometer. Radiation lights having radiants such as the upper portion of the side wall of the crucible 11, the heater 12, the heat insulating mold 13, and the lower chamber's upper wall 14a, which surround the melt surface 17a and are hot, provide a specular reflection on the melt surface 17a. Therefore, even when the temperature of the melt surface 17a in the vicinity of the single crystal 18 is directly measured using the radiation thermometer, the radiation lights caused by specular reflection (hereinafter, referred to as the stray lights) are incident on the radiation thermometer, in addition to the thermal radiation light from the melt surface 17a itself, so that an error in the measured temperature is easily caused.
In order to reduce the influence of the stray light and improve the measurement precision, various kinds of temperature measuring devices were proposed.
FIG. 2 is a diagrammatic sectional view showing an apparatus 50 for pulling a single crystal incorporating a conventional temperature measuring device 55 (Japanese Kokai No. 58-168927), and reference numeral 14a represents a lower chamber's upper wall. A window 19 facing the melt surface 17a in the vicinity of a single crystal 18 is formed at a prescribed place on the lower chamber's upper wall 14a, and is sealed with a quartz glass member 19a or the like.
On the other hand, a polarizing filter 51 and an optical detecting means (silicon electromotive force device) 52 are arranged above the window 19 in a slanting direction on the axis 54 of a radiation light. The optical detecting means 52 is connected through an amplifier 53 to an electric power supply regulator 12a. The temperature measuring device 55 includes the polarizing filter 51, the optical detecting means 52, and the amplifier 53.
In the temperature measuring device 55 having the above construction, a stray light component is rejected by separating to measure a component S.sub.1 polarized in parallel to the melt surface 17a and a component S.sub.2 polarized vertically (neither of them shown) and performing a computation of (S.sub.1 +S.sub.2) -.alpha.(S.sub.1 -S.sub.2). Here, .alpha. is a function related to a measurement wavelength region, an angle of reflection, and the like. Practically, the value is experientially selected.
Since the other constituents are almost the same as those of the apparatus for pulling a single crystal 40 shown in FIG. 1, detailed descriptions thereof are omitted here.
FIG. 3 is a diagrammatic sectional view showing an apparatus 60 for pulling a single crystal incorporating a temperature measuring device 62 which was previously proposed by the present inventors (Japanese Kokai No. 06-129911), and reference numeral 15 in the figure represents an upper chamber's wall. A window 61 facing downward in a slanting direction is formed at a prescribed place on the side wall 15a of the upper chamber's wall 15, and is sealed with a quartz glass member 61a or the like.
A temperature measuring auxiliary plate 63 is held at a prescribed place on the inner surface of the lower chamber's upper wall 14a. The temperature measuring auxiliary plate 63 is made of a graphite material or the like whose emissivity is known and has low angle-dependence. On the other hand, a radiation thermometer 64 and a dichroic radiation thermometer 65 are arranged above the windows 19 and 61 in a slanting direction, respectively. The radiation thermometer 64 is placed on the axis of a thermal radiation light 67a radiated from a measurement point A on the melt surface 17a, while the dichroic radiation thermometer 65 is placed on the axis of a radiation light 67b radiated from a radiant B on the temperature measuring auxiliary plate 63. The mounting positions and angles of the temperature measuring auxiliary plate 63, the radiation thermometer 64, and the dichroic radiation thermometer 65 are selected respectively so that the radiation light 67c radiated from the radiant B is reflected from the measurement point A and that the reflected light (stray light) 67d is incident on the radiation thermometer 64 in conjunction with the thermal radiation light 67a. The radiation thermometer 64 and the dichroic radiation thermometer 65 are connected to a computing means 66 which is connected to an electric power supply regulator 12a. The temperature measuring device 62 includes the temperature measuring auxiliary plate 63, the radiation thermometer 64, the dichroic radiation thermometer 65, and the computing means 66.
In the temperature measuring device 62 having the above construction, the luminance of a radiation light 67 which is the reflected light 67d integrated with the thermal radiation light 67a radiated from the measurement point A is measured using the radiation thermometer 64, and the luminance signal 68 is transmitted to the computing means 66. At the same time, the temperature signal 69 of the radiant B measured using the dichroic radiation thermometer 65 is transmitted to the computing means 66. In the computing means 66, the luminance of the radiation light 67b radiated from the radiant B is computed with the data of the temperature signal 69, and the luminance of the radiation light 67b is subtracted from that of the radiation light 67 to obtain that of the thermal radiation light 67a. The temperature of the measurement point A on the melt surface 17a is detected by computation with the luminance data of the thermal radiation light 67a.
Since the other constituents are almost the same as those of the apparatus for pulling a single crystal 50 shown in FIG. 2, detailed descriptions thereof are omitted here.
FIG. 4 is a diagrammatic sectional view showing an apparatus for pulling a single crystal 70 incorporating a temperature measuring device 71 which was previously proposed by the present inventors (Japanese Kokai No. 08-74979), and reference numeral 14a in the figure represents a lower chamber's upper wall. A stray light rejecting plate 72 is held at a prescribed place on the under surface of the lower chamber's upper wall 14a. The stray light rejecting plate 72 is made of a graphite material or the like, which has a relatively low emissivity and does not easily contaminate a melt 17 as an impurity. A cooling means (not shown) is mounted near the mounting place of the stray light rejecting plate 72 on the lower chamber's upper wall 14a. By operating the cooling means, the temperature of the stray light rejecting plate 72 is kept at a prescribed temperature or below at all times.
On the other hand, a radiation thermometer 73 is arranged above a window 19 in a slanting direction, and is placed on the axis of a thermal radiation light 75a radiated from a measurement point A on the melt surface 17a. The mounting positions and angles of the stray light rejecting plate 72 and the radiation thermometer 73 are respectively selected so that a radiation light 75b radiated from a radiant B on the stray light rejecting plate 72 is reflected from the measurement point A and so that the reflected light (stray light) 75c is incident on the radiation thermometer 73 in conjunction with the thermal radiation light 75a. The radiation thermometer 73 is connected to a computing means 74 which is connected to an electric power supply regulator 12a. The temperature measuring device 71 includes the stray light rejecting plate 72, the radiation thermometer 73, and the computing means 74.
In the temperature measuring device 71 having the above construction, the luminance of the radiation light 75 which is the reflected light 75c integrated with the thermal radiation light 75a radiated from the measurement point A, is measured using the radiation thermometer 73, and the luminance signal 76 is transmitted to the computing means 74. At that time, by cooling the radiant B beforehand to a prescribed temperature (e.g. 800.degree. C. when the melt 17 is Si) or below, the luminance of the reflected light 75c becomes so small that it can be neglected. Therefore, even if the luminance of the radiation light 75 is used for a computation in the computing means 74, a quite accurate temperature of the measurement point A on the melt surface 17a can be obtained.
Since the other constituents are almost the same as those of the apparatus 50 for pulling a single crystal shown in FIG. 2, detailed descriptions thereof are omitted here.
In the temperature measuring device 55 shown in FIG. 2. a function .alpha. is experientially selected, so that it is difficult to certainly reject a stray light component to accurately measure the temperature of the melt surface 17a.
In the temperature measuring device 62 shown in FIG. 3. both of the radiation thermometer 64 and the dichroic radiation thermometer 65 are required for an apparatus for pulling a single crystal 60, leading to a high cost.
In the temperature measuring device 71 shown in FIG. 4, the cooling means need be mounted on the lower chamber's upper wall 14a. An existing apparatus for pulling a single crystal would need to be extensively modified, which is an inconvenience.